In determining uplink (UL) power requirements for a transceiver, it is possible to examine received downlink (DL) signals and extract at least some of the information required to determine the proper UL transmission power since there is typically a proportionality between the received signal power and the power necessary to transmit. If the transmission power of a signal received at the transceiver is known, or if there is some way to estimate the transmission power, the necessary transmission power to reply to that transmission can be estimated.
However, for certain types of communication systems, such as time slotted communication systems, these estimates may be very inaccurate. This is because the accuracy of signal level measurements is affected by the duration of the measurement and the elapsed time since the measurement was last taken. If the duration of the measurement is too short, variations in the measured signal level adversely affect the measurement. If the elapsed time is too long, the measurement becomes less representative of the present state of the signal level due to interim changes in the signal.
For example, in the case of a wireless transmit/receive unit (WTRU) on a time division duplex (TDD) or time division synchronous code division multiple access (TD-SCDMA) system, the power of the transmission may vary greatly both between timeslots, or even within a timeslot. This power variation is affected by various factors, most notably the physical movement of the WTRU. For example, if a WTRU is moving at a moderate pace, such as 60 km/h, it is possible to lose significant signal power in several tens of milliseconds. If a radio frame is 10 ms long, this means that significant signal variations can occur even within the frame. Therefore, it is of prime importance that path loss measurements be applied as fast as practical since an instantaneous measurement of signal characteristics can quickly lose its validity. It is very difficult to find a reference with which to base power adjustments and control.
In the DL of many current wireless communication systems, there is at least one beacon signal or pilot signal that is transmitted to all of the WTRUs. If the wireless communication system is a time-slotted system, there is at least one beacon signal in each frame. This is the case with a Universal Mobile Telecommunication System (UMTS), which uses the beacon signal for path loss measurements.
For example, in TDD and TD-SCDMA systems, the WTRU measures the received signal code power (RSCP) of the serving cell's primary common control physical channel (P-CCPCH) or other beacon channel each frame or sub-frame, and calculates the path loss between the Node B and the WTRU. This has the advantage of providing an accurate path loss measurement immediately after the beacon signal is transmitted. The path loss measurement based on the RSCP is used to determine the transmit power for UL physical channels. Examples of such UL physical channels include the physical random access channel (PRACH), the dedicated physical channel (DPCH), the physical uplink shared channel (PUSCH), and the high speed shared information channel (HS-SICH).
In TDD systems, open-loop power control for UL transmissions based upon DL path loss estimations is commonly employed. TD-SCDMA systems usually employ an open-loop power control for setting of UL initial transmission power before transitioning into closed-loop power control mode, or for reverting back into open-loop power control mode.
It would therefore be desirable to provide a method for performing path loss estimation without the disadvantages of known prior art channel estimation methods.